From DE 32 42 789 C1 there is known an apparatus for checking sheet material having a plurality of sensors arranged along a sensor path along which the bank notes are transported. The sensors each have two components which are arranged at opposite sides of the bank note transport path. The components of various sensors which are arranged on one side of the transport path are jointly mounted on one mounting plate, one of the mounting plates being pivotally supported so that the sensor path can be exposed e.g. for maintenance purposes. For mounting, the two mounting plates, on which sensor components are located opposite each other, can be connected with each other for example via a hinge. Besides the mechanical play in the hinge, the mounting parts of the mounting plates and the two mounting plates, too, have tolerances. Because of the tolerances, normally, an exact alignment of the upper sides of the mounting plates carrying the sensor components cannot be achieved. Even when tilting one of the mounting plates, for example for exposing the sensor path, out of the operating position and then back again, normally, they cannot be arranged in exactly the same position again. Instead, a slightly changed operating position of the mounting plate and thus the sensor components is the result. The relative position of components of a sensor located opposite each other and mounted on different mounting plates, therefore, is subject to a fluctuation which can lead to a maladjustment of the two components and impair the function of the sensor.